Method and apparatus for pouring liquid metal into a continuous-casting mold

ABSTRACT

A method and apparatus for pouring a stream of liquid metal into a continuous-casting mold. A body which has a convexly curved surface (for example a sphere) and is of essentially inert material floats in the pool of liquid metal in the mold. As a stream of liquid metal is poured into the mold, it impinges on the surface of the floating body and thus enters the pool in a quiescent state. The body remains centered under the stream through the action of natural forces.

United States Patent [1 1 Griffiths METHOD AND APPARATUS FOR POURING LIQUID METAL INTO A CONTINUOUS-CASTING MOLD Inventor: David K. Griffiths,Penn Hills Township, Allegheny County, Pa.

Assignee: United States Steel Corporation,

Pittsburgh, Pa.

Filed: June '29, i971 Appl. No.: 158,028

Int. Cl. .Q ..B22d 11/10 Field of Search ..l64/82, 133, 136,

References Cited UNITED STATES PATENTS 1,961,529'v 6/1934 Rowe ..l64/l36X 2,243,425 5/1941 Junghans ..l64/82 vs. Cl ...164/s2 164/281 5 1 Apr. 17, 1973 2,305,477 12/1942 Junghans [64/82 X 2,366,289 l/l945 Rowe 3,050,792 8/ I962 Lipman et al 164/136 X FOREIGN PATENTS on APPLICATIONS 750,989 2/1954 Germany ..l64/82 Primary Examiner-R. Spencer Annear Attorney-Walter P. Wood [57] ABSTRACT A method and apparatus for pouring a stream of liquid metal into a continuous-casting mold. A body which has a convexly curved surface (for example a sphere) and is of essentially inert material floats in the pool of liquid metal in the mold. As a stream of liquid metal is poured into the mold, it impinges on the surface of the floating body and thus enters the pool in a quiescent I state. The body remains centered under the stream through the action of natural forces.

5 Chins, 2 Drawing Figures METHOD AND APPARATUS FOR POURING LIQUID METAL INTO A CONTINUOUS-CASTING MOLD This invention relates to an improved method and apparatus for pouring a stream of liquid metal into a continuous-casting mold.

In a conventional continuous-casting operation, liquid metal is poured through an open-ended, vertically oscillating, water-cooled mold. A partially solidified casting emerges continuously from the lower end of the mold, and travels through a secondary cooling zone, where it solidifies throughout. The mold contains a pool of liquid metal and a solidified skin which surrounds the pool at the mold wall and becomes progressively thicker toward the lower end. When metal is poured through air into the pool, some air is entrained in the pouring stream and carried into the pool as bubbles. Oxygen in the bubbles forms metallic oxides, which are carried deeply into the pool and are frozen in place as nonmetallic inclusions to the detriment of the cast product.

Knownsolutions to this problem are either to shroud the pouring stream with an inert gas, or to pour through an extended nozzle, the lower end of which is immersed in the pool. Shrouding with inert gas is not altogether satisfactory in preventing formation of oxide inclusions, besides which any slag floating on the pool may be entrained and carried into the casting. Use of an extended nozzle leads to many difficulties. If the upper end of the nozzle is not properly sealed to the pouring vessel, the stream of metal may aspirate air. Frequently a skull forms on the lower end of the nozzle. The pouring stream always penetrates deeply into the pool and thus carries superheated metal to a level where it may erode the solidified skin of the casting. Such erosion is at least a contributing cause of longitudinal cracking which sometimes occurs in the casting.

An object of my invention is to provide an improved pouring method and apparatus which largely overcome the foregoing difficulties.

A further object is to provide an improved method and apparatus for pouring liquid metal into a continuous casting moldin which I may expose a liquid metal stream to air but limit penetration .of air bubbles into the pool ofliquid metal in the mold.

t A more specific object is to provide an improved pouring method and apparatus applicable to continuous casting wherein an essentially inert body having a convexly curved surface floats freely in the pool of liquid metal in a mold, and the incoming stream of metal impinges on the body and thereby enters the pool in a quiescent state.

In the drawing:

FIG. 1 is a diagrammatic vertical section of a continuous-casting mold and pouring vessel equipped with my improved apparatus; and

FIG. 2 is a side elevational view ofa body of modified (not shown). Within the mold the liquid metal forms a pool 15. A skin 16 solidifies at the mold wall and becomes progressively thicker toward and beneath the lower end of the mold. The partially solidified casting which results emerges continuously from the lower end of the mold for further processing, as known in the art.

In accordance with my invention, I place a floating body 17 in the pool 15 in a position where the stream 13 impinges on its upper surface. FIG. 1 shows a spherical body, but I can use bodies of other configuration as long as the surface is curved convexly. One such example is a cylindrical body 17a with rounded ends, as

shown in FIG. 2. The body is of a material essentially inert to the metal of the pool and stream, preferably a refractory. Preferably the body has a specific gravity about half that of the metal, thus enabling it to float in a position where it is approximately at least half submerged. A'body which floats higher lacks stability, and a disturbance in the pouring stream 13 may force it out of range of the stream. Increasing the specific gravity of the body has no detrimental effect until the body becomes so heavy that the force of the stream fully submergesit in the pool. The body may have a high-density core 18, if the refractory alone has a specific gravity which is too low. If the body is approximately spherical as illustrated in FIG. 1, its diameter. should be about one-half to two-thirds the minimum inside horizontal dimension of mold 14. A body which is too big may be entrapped between the solidifying fronts of the skin 16 of the casting.

In operation, I start the cast in the usual way without the body 17 or 17a. Preferably, l] preheat the body to prevent its spalling or skulling. Once the cast is underway, I place the body in the pool 15 and nudge it into a position where the stream 13 impinges against its surface. Natural forces automatically center the body under the stream, a phenomenon. easily demonstrated by floating a rubber ball on a pool of water and directing a stream from a hose against its surface. The one limitation is that the body must be brought intocontact with the stream; without contact the body does not seek the stream. a

The metal flows smoothly over the convex surface of the body which dissipates its energy, whereby themeal enters the pool in a quiescent state. The body prevents deep penetration of the pouring stream into the pool. Even though the stream may be exposed to air, the body prevents deep penetration of bubbles which form oxide inclusions into the casting. The distance between the surface of the body and the bottom of nozzle 12 is not critical. If there is more than one stream of 'metal going into themold, I may place separate bodies under each stream. Alternatively, I may use a cylindrical body 17a which is sufficiently long to intercept all the pouring streams in a line. The cylinder likewise is stabilized under the multiplicity of pouring streams. It is apparent also that I may use the body with a metal stream which is shrouded with inert gas. I

My invention is. to' be distinguished from the' use heretofore of floating bodies as splash-prevention devices in ingot molds, as shown for example in Gersioned accurately in accordance with the mold dimensions. This arrangement is not suited for continuous casting.

I claim:

l. A method of pouring liquid metal into a continuous-casting mold, wherein a stream of metal enters the mold from a source thereabove, and liquid metal from said source forms a pool within the mold, said method comprising floating an approximately spherical body in said pool, said body having a diameter about one-half to two-thirds the minimum inside horizontal dimension of said mold and being of a material essentially inert to said metal, and impinging said stream on the surface of said body whereby said body automatically centers itopening in its bottom wall, a continuous-casting mold positioned below said vessel, said opening being adapted to discharge a stream of liquid metal into said mold where it forms a pool, and an approximately spherical body floating in said pool in a position where said stream impinges on its surface, said body having a diameter about one-half to two-thirds the minimum inside dimension of said mold and being of a material essentially inert to said metal.

3. A method as defined in claim 1 in which the minimum specific gravity of said body is approximately half that of the metal.

4. A method as defined in claim 1 in which said body is preheated before it is introduced to said pool.

5. -A combination as defined in claim 2 in which the minimum specific gravity of said body is approximately half that of the metal. 

1. A method of pouring liquid metal into a continuous-casting mold, wherein a stream of metal enters the mold frOm a source thereabove, and liquid metal from said source forms a pool within the mold, said method comprising floating an approximately spherical body in said pool, said body having a diameter about one-half to two-thirds the minimum inside horizontal dimension of said mold and being of a material essentially inert to said metal, and impinging said stream on the surface of said body, whereby said body automatically centers itself under said stream and causes the metal to enter said pool in a quiescent state without deeply penetrating the pool.
 2. In combination, a pouring vessel having a pour opening in its bottom wall, a continuous-casting mold positioned below said vessel, said opening being adapted to discharge a stream of liquid metal into said mold where it forms a pool, and an approximately spherical body floating in said pool in a position where said stream impinges on its surface, said body having a diameter about one-half to two-thirds the minimum inside dimension of said mold and being of a material essentially inert to said metal.
 3. A method as defined in claim 1 in which the minimum specific gravity of said body is approximately half that of the metal.
 4. A method as defined in claim 1 in which said body is preheated before it is introduced to said pool.
 5. A combination as defined in claim 2 in which the minimum specific gravity of said body is approximately half that of the metal. 